In a large mass-production operation, such as the manufacture of motor vehicles, it is standard practice to use a stepping or shuttle-type conveyor. The workpieces sit on the shuttles of the conveyor that transports them in steps through a concatenation or row of working stations. A machine or worker at each station performs an operation--welding, boring, tapping, painting, pressing, or the like--on the respective workpiece.
When the workpieces are large they are usually completely freed from the conveyor in each station, providing the opportunity for the unloaded conveyor to move a step back upstream prior to stepping the workpieces one more station downstream. Such removal is often required to ensure perfect positioning of the workpieces for the particular manufacture operation of the station.
This style of production is wholly unsuitable for small production runs, as retooling and changing the various machines to do different things or to work on different workpieces is an extremely onerous and time-consuming job. In fact it is not uncommon for a production line to be down for six months for a model change in the automotive industry.
It is known in small manufacturing operations to use a flexible conveyor system that allows stations to be skipped, or even different paths to be followed, and can even do different jobs at each station by using multiduty machines at some of the stations. Such a conveyor is extremely complex and expensive. Although it does make changing a production run much simpler, its cost cannot be justified when such a change is not done often.